1. Field of the Invention (Technical Field)
The present invention relates to circular antenna polarization for radio detecting and ranging (RADAR) applications, particularly in conjunction with active electronically steerable arrays (AESAs).
2. Description of Related Art
In the lower portion of the RF spectrum (Ku-band and below), coaxial and wave guide connections dominate the RADAR interconnectivity scheme. However, as RADAR system development is pushed into millimeter wave (mmwave) frequencies and above, coaxial interconnection is no longer feasible while the form-factor associated with wave guide is often impractical for small integrated assemblies.
Therefore, one of the greatest challenges in miniaturizing RADAR module assemblies at mmWave frequencies is achieving a functional, low loss RF interface between the exciter, feed, and antenna networks (functions that usually exist in planes orthogonal to one another).
Circular polarization at mmWave has most recently been achieved by implementing difficult, low yield orthogonal RF transitions to make the interface between the module's planar RF exciter and feed circuitry (existing in the x-y plane) and antenna elements (existing in the y-z plane). These transitions have been achieved by employing relatively expensive and problematic specialty coaxial connections or fin-line transmission lines. Both techniques, however, have a relatively high degree of difficulty associated with manufacturing them while the coaxial technique is currently frequency limited to Ka-band and below.
A cross slot circularly polarized antenna has been proposed, but in addition to becoming impractically small at mmWave frequencies, it too requires an orthogonal RF transition and thus suffers from the same manufacturing difficulties.